The present invention relates generally to switch circuitry and, more particularly, to a switch circuit for a transceiver, such as a transceiver operable to transmit and to receive communication signals during alternate time periods.
A communication system is comprised, at a minimum, of a transmitter and a receiver interconnected by a communication channel. A communication signal is transmitted by the transmitter upon the transmission channel to be received by the receiver. A radio communication system is a communication system in which the transmission channel comprises a radio frequency channel defined by a range of frequencies of the electromagnetic frequency spectrum. A transmitter operative in a radio communication system must convert the communication signal into a form suitable for transmission upon the radio-frequency channel.
Conversion of the communication signal into a form suitable for transmission upon the radio-frequency channel is effectuated by a process referred to as modulation. In such a process, the communication signal is impressed upon an electromagnetic wave. The electromagnetic wave is commonly referred to as a "carrier signal." The resultant signal, once modulated by the communication signal, is commonly referred to as a modulated carrier signal. The transmitter includes circuitry operative to perform such a modulation process.
Because the modulated carrier signal may be transmitted through free space over large distances, radio communication systems are widely utilized to effectuate communication between a transmitter and a remotely-positioned receiver.
The receiver of the radio communication system which receives the modulated carrier signal contains circuitry analogous to, but operative in a manner reverse with that of, the circuitry of the transmitter and is operative to perform a process referred to as demodulation.
Numerous modulated carrier signals may be simultaneously transmitted upon differing radio frequency channels of the electromagnetic frequency spectrum. Regulatory bodies have divided portions of the electromagnetic frequency spectrum into frequency bands, and have regulated transmission of the modulated carrier signals upon various ones of the frequency bands. (Frequency bands are further divided into channels, and such channels form the radio-frequency channels of a radio communication system. Such channels shall, at times, be referred to hereinbelow by the term conventionally-defined frequency channels.)
A two-way radio communication system is a radio communication system, similar to the radio communication system above-described, but which permits both transmission and reception of a modulated carrier signal from a location and reception at such location of a modulated carrier signal. Each location of such a two-way radio communication system contains both a transmitter and a receiver. The transmitter and the receiver positioned at a single location typically comprise a unit referred to as a radio transceiver, or more simply, a transceiver.
A cellular communication system is one type of two-way radio communication system in which communication is permitted with a radio transceiver positioned at any location within a geographic area encompassed by the cellular communication system.
A cellular communication system is created by positioning a plurality of fixed-site radio transceivers, referred to as base stations or base sites, at spaced-apart locations throughout a geographic area. The base stations are connected to a conventional, wireline telephonic network. Associated with each base station of the plurality of base stations is a portion of the geographic area encompassed by the cellular communication system. Such portions are referred to as cells. Each of the plurality of cells is defined by one of the base stations of the plurality of base stations, and the plurality of cells together define the coverage area of the cellular communication system.
A radio transceiver, referred to in a cellular communication system as a cellular radiotelephone or, more simply, a cellular phone, positioned at any location within the coverage area of the cellular communication system, is able to communicate with a user of the conventional, wireline, telephonic network by way of a base station. Modulated carrier signals generated by the radiotelephone are transmitted to a base station, and modulated carrier signals generated by the base station are transmitted to the radiotelephone, thereby to effectuate two-way communication therebetween. (A signal received by a base station is then transmitted to a desired location of a conventional, wireline network by conventional telephony techniques. And, signals generated at a location of the wireline network are transmitted to a base station by conventional telephony techniques, thereafter to be transmitted to the radiotelephone by the base station.)
Increased usage of cellular communication systems has resulted, in some instances, in the full utilization of every available transmission channel of the frequency band allocated for cellular radiotelephone communication. As a result, various ideas have been proposed to utilize more efficiently the frequency band allocated for radiotelephone communications. By more efficiently utilizing the frequency band allocated for radiotelephone communication, the transmission capacity of an existing, cellular communication system may be increased.
The transmission capacity of the cellular communication system may be increased by minimizing the modulation spectrum of the modulated signal transmitted by a transmitter to permit thereby a greater number of modulated signals to be transmitted simultaneously. Additionally, by minimizing the amount of time required to transmit a modulated signal, a greater number of modulated signals may be sequentially transmitted.
By converting a communication signal into discrete form prior to transmission thereof, the resultant modulated signal is typically of a smaller modulation spectrum than a corresponding modulated signal comprised of a communication signal that has not been converted into discrete form. Additionally, when the communication signal is converted into discrete form prior to modulation thereof, the resultant, modulated signal may be transmitted in short bursts, and more than one modulated signal may be transmitted sequentially upon a single, conventionally-defined, frequency channel. (As more than one modulated signal may be transmitted upon a single, conventionally-defined, frequency channel, the term frequency channel is sometimes referred to as the portion of the conventionally-defined frequency channel during which a particular transmitter transmits a modulated signal to a particular receiver. Hence, in a communication scheme in which modulated signals are transmitted in discrete bursts, two or more frequency channels may be defined upon a single, conventionally-defined, frequency channel.)
As a single frequency channel is utilized to transmit two or more separate signals during nonoverlapping time periods, a method of signal transmission is referred to as a time division method. A communication system incorporating such a time division method of signal transmission includes a Time Division Multiple Access communication system or, more simply, a TDMA communication system.
A TDMA communication system includes a transmitter operative to transmit signals to a receiver in intermittent bursts during intermittent time periods. Such signal transmitted to a particular receiver operative in a TDMA communication system shall hereinafter be referred to as a TDMA signal.
A TDMA communication system is advantageously utilized as a cellular communication system as, during time periods in which a base station does not transmit a TDMA signal to a particular radiotelephone, other TDMA signals may be transmitted. In particular, the radiotelephone to which the base station transmits a TDMA signal may, in turn, transmit a TDMA signal to the base station, thereby permitting two-way communication between the base station and the radiotelephone upon a single, conventionally-defined frequency channel as signals transmitted to the radiotelephone by the base station, and by the radiotelephone to the base station may be timed to occur during alternate time periods.
As the transmitter and receiver circuitry portions of the radiotelephone operative in such a TDMA communication system are required to be operable only during alternate time periods, certain circuitry portions of radiotelephones operable in conventional, cellular communication systems are not required. For instance, duplexer filters positioned to interconnect both the transmitter circuitry portion and the receiver circuitry portion of the conventional, cellular radiotelephone and the radiotelephone antenna theretogether, are not required to form portions of radiotelephones operable in a TDMA communication system as the receiver and transmitter circuitry portions of such radiotelephone need not be operable simultaneously. Rather, switch circuitry may be utilized alternately to connect the receiver circuitry portion with the radiotelephone antenna or the transmitter circuitry portion with the radiotelephone antenna.
Conventional switch circuitry utilized alternately to connect the receiver circuitry portion or the transmitter circuitry portion with the radiotelephone antenna have been comprised of discrete, component elements or, discrete, component elements together with conventional transmission lines. In general, such switch circuits are operable alternately to connect electrically either the receiver or transmitter circuitry portion of the radiotelephone to the radiotelephone antenna while also electrically isolating the other of the radiotelephone circuitry portion from the radiotelephone antenna.
However, either of such constructions of switch circuits include circuit elements which are of low relative quality factors (Q factors values) and, hence, exhibit significant amounts of insertion loss. Hence, while such circuits are oftentimes represented with idealized elements, parasitic effects caused as a result of stray capacitances and inductances cause such switch circuits to be inherently inefficient. To overcome such inefficiency of the conventional switch circuits, amplifier portions of the transmitter circuitry portion of the radiotelephone must amplify signals which are to be transmitted at greater amplification levels. Such greater amplification levels, however, result in increased energy consumption of the radiotelephone.
A switch circuit exhibiting a lesser amount of insertion loss would permit lesser amounts of energy to be consumed during operation of the radiotelephone.
What is needed, therefore, is a switch circuit exhibiting a lesser amount of insertion loss than the amount of insertion loss exhibited by conventional, switch circuits.